This invention relates to a halogen-containing thermoplastic resin composition excelling in processability, appearance, strength, hydrophilicity, resistance to oil and solvents and gas barrier property.
Halogen-containing thermoplastic resins, represented by polyvinyl chloride, are not only comparatively inexpensive but also have excellent clarity and mechanical properties and have therefore been used in a variety of applications, such as film, sheet, hose, flexible containers, coated fabric, artificial leather, tarpaulin, shoe bottom, sponge, electrical wire sheathing, living necessaries and so on.
Having the above-mentioned advantages on the one hand, halogen-containing thermoplastic resins are disadvantages, on the other hand, in that they are not satisfactory in processability, hydrophilicity, resistance to oil and solvents, gas barrier property and adhesiveness to substrates.
In order to improve the processability, hydrophilicity and other properties of halogen-containing thermoplastic resins, it has been practiced to polymer-blend these resins with a modifying resin such as a hydrolyzed ethylene-vinyl acetate copolymer.
By way of example, Japanese Patent Application KOKAI No. 69955/1977 discloses a polyvinyl chloride barrier packaging composition essentially comprising a mixture of a vinyl chloride polymer and an ethylene-vinyl alcohol copolymer, the proportion of which is 10 to 30 weight percent based on the vinyl chloride polymer.
Japanese Patent Application KOKAI No. 238345/1985 describes a resin composition comprising (a) a thermoplastic resin (including polyvinyl chloride), (b) a hydrolyzed ethylene-vinyl acetate copolymer, and (c) a salt or an oxide containing at least one element selected from the group consisting of the elements of Groups I, II and III of Periodic Tables of the Elements and mentions that this composition has remarkably improved compatibility.
However, although the addition of a hydrolyzed ethylene-vinyl acetate copolymer to a halogen-containing thermoplastic resin results in improvements in hydrophilicity, resistance to oil and solvents and gas barrier property, the inherent poor compatibility of the two resins makes long-run molding difficult and, moreover, the products obtainable therefrom by melt-molding have foreign matter and discoloration problems and poor mechanical properties.
The composition according to Japanese Patent Application KOKAI No. 238345/1985 referred to above has improved compatibility but the degree of improvement by addition of salt or oxide has its own limit and it still has much room for improvement.
The object of this invention is to solve the above-mentioned problems by employing a specific vinyl chloride graft polymer in adding a vinyl alcohol polymer to a halogen-containing thermoplastic resin for improving its properties.